Light emitting device

ABSTRACT

A technique for sealing an EL panel of a light emitting device is provided. By preparing a absorption metal as a film on EL elements on the inside of an enclosed space, it becomes easy to made the interior of the space possess a absorption function, and further, an enclosure structure can be fabricated without the penetration of oxygen and moisture into the space because the absorption film is formed in succession after formation of the EL elements, according to the present invention.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 09/966,740, filed Oct. 1, 2001 now U.S. Pat. No. 6,924,594, nowallowed which claims the benefit of a foreign priority application filedin Japan as Ser. No. 2000-304246 on Oct. 3, 2000. This applicationclaims priority to each of these prior applications, and the disclosuresof the prior applications are considered part of (and are incorporatedby reference in) the disclosure of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device (hereinafter referred to as alight emitting device) formed by building an EL (electroluminescence)element on a substrate. In particular, the present invention relates toa sealing technique for an EL panel of a light emitting device in whichEL elements formed on a substrate are sealed. Note that a module inwhich an FPC is connected to an EL panel, and an IC (integrated circuit)is directly mounted through the FPC, is referred to as a light emittingdevice within this specification.

2. Description of the Related Art

Research into light emitting devices having EL elements as lightemitting elements has been active in recent years, and in particular,light emitting devices using organic materials as EL materials havereceived a lot of attention. These types of light emitting devices arereferred to as organic EL displays (OELDs) or organic light emittingdiodes (OLEDs).

Light emitting devices do not have viewing angle problems because theyare self light emitting unlike liquid crystal display devices. Namely,light emitting devices are more suitable for use out of doors thanliquid crystal displays, and a variety of usages have been proposedtherefor.

EL elements are structured by an EL layer sandwiched between a pair ofelectrodes, and the EL layer normally has a lamination structure. Atypical lamination structure proposed by Tang, et al., of Eastman KodakCo., has a lamination structure made from a hole transporting layer, alight emitting layer, and an electron transporting layer. This structurehas extremely high light emitting efficiency, and nearly all lightemitting devices currently undergoing research and development employthis structure.

Further, additional structures may also be used in which a holeinjecting layer, a hole transporting layer, a light emitting layer, andan electron transporting layer are laminated on an anode in the statedorder; or in which a hole injecting layer, a hole transporting layer, alight emitting layer, an electron transporting layer, and an electroninjecting layer are laminated on an anode in the stated order, may alsobe used. An element such as a fluorescing pigment may also be doped intothe light emitting layer. Further, the layers may all be formed by filmscomposed of low molecular weight materials, or they may all be formed byfilms composed of high molecular weight materials.

All layers formed between the anode and the cathode are definedgenerically as EL layers within this specification. Therefore, layersdescribed above, namely the hole injecting layers, electron injectinglayers, hole transporting layers, light emitting layers and electrontransporting layers are all included in EL layers.

Note that a light emitting element formed by a cathode, an EL layer, andan anode is referred to as an EL element within this specification, andthat there are two types of formation methods: a method of forming ELlayers between two types of stripe shape electrodes formed to bemutually orthogonal (simple matrix method), and a method of forming ELlayers between pixel electrodes and opposing electrodes arranged in amatrix shape and connected to TFTs (active matrix method).

Among EL elements, those using fluorescent organic compounds in their ELlayers are referred to as organic EL elements, and the biggest problemin putting them to practical use is that the lifetime of the elements isinsufficient. Further, element deterioration appears as a widening ofnon-light emitting regions (dark spots) accompanying long light emissiontime, and the major cause of this deterioration is due to cathodepeeling.

The development of dark spots due to causes such as cathode oxidationand peeling often results from oxygen and moisture within theatmosphere. For example, it is possible to operate elements within theatmosphere if an electrode manufactured by a stable metal such as anMgAg composite is used, but the life of the elements is shortened. It istherefore ideal to perform manufacture of elements all at once in avacuum or within a glove box under an inert gas atmosphere in order toobtain good element properties.

Namely, the sealing technique used becomes crucial in the manufacture ofelements possessing sufficient lifetime for practical usage. A method inwhich elements are covered by a glass substrate under a dry nitrogen orinert gas atmosphere to seal the periphery by a resin is generallyemployed.

However, the development of dark spots has been observed even on sealingsubstrates. It is thought that this is due to promotion of a chemicalreaction occurring between the electrodes and residual impurities due toa high electric field produced when driving the elements. In otherwords, matter adsorbed on the surface and matter emitted from the resinused in sealing exists even if the purity of the gas to be introduced ishigh, and therefore it is difficult to completely eliminate substancessuch as oxygen and moisture. The method shown below has been devised inview of this problem.

A cross sectional structure of a general EL panel seal is shown in FIG.16. Reference numeral 1601 denotes a substrate in FIG. 16, referencenumeral 1602 denotes an anode, reference numeral 1603 denotes an ELlayer, and reference numeral 1604 denotes a cathode. The anode 1602 andthe cathode 1604 are each electrically connected to an external powersource. An EL element on the substrate 1601 composed of the anode 1602,the EL layer 1603, and the cathode 1604 is then sealed by a sealingsubstrate 1607, through a sealant 1608.

An absorption agent (also referred to as a water capturing agent) 1606made from an absorption substance is added here in order to preventdeterioration of the EL element due to oxygen and moisture existing in aspace 1609. This is discussed in detail in the following reference.(Reference: Shin Kawami, Takemi Naito, Hiroshi Ohata, Jin Nakata,“Effect of Water Capturing Agents in Enclosing of Organic EL Elements”,The 45th Japan Society of Applied Physics Proceedings, p. 1223 (1998).

Note that as the absorption agent, there may be used physical absorptionsubstances, typically silica gel, synthetic zeolites, and the like, andchemical absorption substances, typically phosphorous pentoxide, calciumchloride, and the like. However, chemical absorption substances take inabsorbed moisture as water of crystallization, and there is nore-emission of moisture, and therefore chemical absorption substancessuch as barium oxide (BaO) are often used.

Further, as for a method of disposing the absorption agent, thegenerally adopted methods include: a method in which a space(depressions) for disposing thereon the absorption agent is formed in asealing substrate, and after placing the absorption agent in the space,a film such as Teflon possessing adhesiveness is bonded thereto in orderto prevent dispersion of the absorption agent; and a method in which abag composed of a permeable substance and filled with the absorptionagent is bonded to a sealing substrate so that the absorption agent doesnot disperse into the space 1609. However, there is also a method inwhich the absorption agent is directly dispersed within the space 1609.

An absorption agent 1606 such as barium oxide is prepared in the space1609, as shown in FIG. 16.

Note that the absorption agent such as barium oxide is normally a solidin a powdered state, and therefore there are adopted a method ofdispersing the absorption agent within the space as it is, or a methodof wrapping this in a film made from a high molecular weight material tobe bonded to a sealing substrate.

Further, since absorption agents are generally introduced by hand, theoperation under an inert gas atmosphere may become more difficult.Further, in a case where it is intended to provide a wrapped absorptionagent, the wrapping itself requires much work.

There are also cases in which introduction of the absorption agent isperformed within the atmosphere due to the complexities of working underan inert gas atmosphere. However, in this case, obviously the problemwith oxygen and moisture being contained within the space 1609 cannot beavoided.

SUMMARY OF THE INVENTION

In consideration of the above, an object of the present invention is toprevent EL element deterioration by providing a structure into whichmoisture and oxygen are not introduced, and by providing a simple andeffective method for adding the absorption agent for absorbing moistureand oxygen, in the sealing of EL elements.

To solve the above problems, according to the present invention,improvements are made with respect to a material having an absorptionproperty which is added, when performing enclosing of El element formedon a substrate, to the inside of the enclosed structure, and a method ofadding the absorption material. Absorption films can thus be easilyformed on EL elements, and in addition, EL element deterioration due tooxygen and moisture is prevented.

In the present invention, first an EL element composed of an anode, anEL layer, and a cathode is formed on a substrate, and then an absorptionfilm is formed on the EL element. Note that the absorption film used inthe present invention is a film formed from a material that is a metalhaving a low work coefficient and which easily oxides in oxygen, and inaddition, the oxide thereof reacts with moisture to form a hydrate,thereby preventing-moisture from being re-emitted. Note also thatalkaline earth metals such as beryllium, magnesium, calcium, strontium,barium, and radium can be used as the metallic material. Further, filmsmade from this type of material is referred to as the absorption filmwithin this specification.

Evaporation and sputtering can be given as methods for forming thesetypes of absorption films, and it is preferable to use a method in whichfilm formation can be performed successively after formation of the ELelements. Further, a resistive evaporation method (RE method) and anelectron beam method (EB method) can be used if evaporation is employed.

Additionally, the absorption films may be formed directly on top of theEL elements, and may also be formed after forming a barrier film madefrom an insulating film such as silicon nitride or silicon oxide on theEL elements in order to prevent direct contact between moisture absorbedby the absorption film, and EL element electrodes.

Further, the absorption film is formed so as to cover the EL elements,and it is necessary to perform film formation selectively using meanssuch as a metal mask so that the EL element are surrounded and so thatthere is no overlap with a sealant applied subsequently.

After forming the absorption film, sealing substrates are prepared inpositions so as to sandwich the EL elements between the sealingsubstrates and the substrate, and a sealant is prepared between thesubstrate and the sealing substrates, forming an enclosure structure.Namely, oxygen and moisture existing in the inside of the enclosurestructure here is captured by the absorption film formed in advance.

Furthermore, it is preferable to use a thermosetting resin or anultraviolet setting resin as the sealant formed here. Note that thesealant is formed so as to surround the absorption agent formed on theEL elements.

The present invention may have a structure in which it is difficult foroxygen and moisture to penetrate to the inside of the enclosurestructure by additionally forming a metallic film or the like so as tocover the sealing substrate and the sealant after forming the aboveenclosure structure.

However, it is necessary in this case to form an insulating film madefrom silicon nitride or silicon oxide in advance on a wiring forelectrically connecting to EL element (electrodes connection wiring)formed on the outside of the enclosure structure. Further, a connectionportion formed in order to connect the EL elements to external drivercircuits must be cutoff by means such as a metal mask, such that ametallic film is not formed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are diagrams for explaining the present invention;

FIG. 2 is a diagram for explaining an element structure of an EL elementin the present invention;

FIG. 3 is a diagram showing an effect of implementing the presentinvention;

FIGS. 4A to 4C are diagrams showing a process of manufacturing a pixelTFT and driver circuit TFTs;

FIGS. 5A to 5C are diagrams showing the process of manufacturing a pixelTFT and driver circuit TFTs;

FIGS. 6A and 6B are diagrams showing the process of manufacturing apixel TFT and driver circuit TFTs;

FIG. 7 is a diagram showing the process of manufacturing a pixel TFT anddriver circuit TFTs;

FIGS. 8A and 8B are diagrams showing an upper surface diagram and anenclosure structure, respectively, of a light emitting device;

FIG. 9 is a diagram showing a cross sectional structure of a passivematrix light emitting device;

FIGS. 10A and 10B are diagrams for showing the enclosing of a lightemitting device;

FIGS. 11A to 11C are photographs showing the deterioration of EL layers;

FIGS. 12A to 12C are photographs showing deterioration of EL layers;

FIG. 13 is a diagram of a film formation apparatus used in forming alight emitting device of the present invention;

FIGS. 14A to 14F are diagrams showing specific examples of electronicequipment;

FIGS. 15A to 15F are diagrams showing specific examples of electronicequipment; and

FIG. 16 is a diagram for explaining a conventional example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Embodiment Mode

A method of sealing EL elements formed on a substrate is explained in anembodiment mode of the present invention.

An upper surface diagram of an EL panel used in the present invention isshown in FIG. 1A, and a cross sectional structure of the EL panel isshown in FIG. 1B.

Reference numeral 101 denotes a substrate, and reference numeral 102denotes a sealing substrate in FIGS. 1A and 1B, and an EL element 106 issandwiched between the substrate 101 and the sealing substrate 102. Notethat the EL element 106 has a structure in which an EL layer 105 isformed between an anode 103 and a cathode 104.

Note also that the anode 103 forming the EL element may be formed bysputtering, and the following can be used as the anode material: ITO, analloy of tin oxide and indium oxide; a chemical compound of 2 to 20% ofzinc oxide (ZnO) mixed into indium oxide); and a chemical compound madefrom zinc oxide and gallium oxide. Further, the cathode 104 can beformed by evaporation using a metal having a low work coefficient, suchas Mg:Ag or Yb. Edge portions of the anode 103 are covered by aninsulating film 110 made from an insulating material.

The EL layer 105 can use a film formation technique such as evaporation,application, or printing. In addition, as a structure of the EL layers,a hole injecting layer, a hole transporting layer, light emittinglayers, electron transporting layers, electron injecting layers, holeblocking layers, and buffer layers can be freely combined and used in alamination structure, or as a single layer structure.

Further, known organic EL materials can be used in the EL layer 105, andeither of high molecular weight (polymer) materials or low molecularweight (monomer) materials may be used. Additionally, a film made from alow molecular weight material and a film made from a high molecularweight material may be laminated to form the EL layer 105.

Note that the present invention can be applied to not only active matrixEL panels but also passive matrix EL panels,.

An absorption film 107 is formed so as to completely cover the ELelement 106 formed on the substrate 101. The absorption film 107 formedhere is formed in succession, after film formation of the EL element106, under an inert gas atmosphere, such as nitrogen or a noble gas.

In addition, an enclosure structure is formed for the sealing substrate102 by a sealant 108 made from a thermosetting resin or an ultravioletlight setting resin. A region surrounded here by the substrate 101 andthe sealing substrate 102 is referred to as a space 109, and the ELelement 106 is positioned on the inside of the space 109 having an inertgas. Note that the sealant is prepared in locations so as not to overlapwith the absorption film.

The arrow in FIG. 1B denotes the direction in which light emitted fromthe EL element 106 is discharged. Namely, as a structure of the ELelement 106, the anode 103 is formed on the substrate 101 side as seenfrom the EL layer 105, and the cathode 104 is formed on the sealingsubstrate 102 side.

By switching the cathode and the anode in the element structure of theEL element, it is possible to reverse the light discharge directioncompared to that of the arrow. However, the transmitting of theabsorption film 107 used in the present invention drops along with theamount of moisture absorbed, and therefore it is preferable to make anelement structure like that shown in FIG. 1B.

Note that a case of forming one EL panel from one substrate is explainedin FIGS. 1A and 1B. It is also possible to apply the present inventionto cases in which a plurality of panels are formed from one substrate.

The absorption film 107 is then formed in succession after forming theEL element 106. The absorption film 107 formed here is formed by a metalhaving a low work coefficient. Note that the term metal having a lowwork coefficient as used herein indicates a metal showing a workcoefficient in a range of 2.0 to 4.0 eV.

Further, considering film formation temperature, it is preferable thatthe absorption film 107 used in the present invention be formed byevaporation. It is also possible to use CVD or sputtering for filmformation provided that low temperature processing is possible.

Next, after the absorption film 107 is formed, enclosure is performedunder an inert gas atmosphere. Materials such as glass, quartz, plastics(including plastic films), metals (typically stainless steel), andceramics can be used as the sealing substrate 102 used in the enclosure.Note that FRP (fiberglass reinforced plastics), PVF (polyvinyl fluoride)films, Mylar films, polyester films, and acrylic resin films can be usedas plastics.

Even if contaminants such as oxygen and moisture are mixed in the spaceformed by enclosure in the above structure, direct intrusion by thecontaminants to the EL element 106 can be prevented with the presentinvention. Preferably, the EL element is enclosed by the substrate andthe absorption film so that the EL element is prevented from contactingthe atmosphere of the space 109. Deterioration of the EL element 106 dueto oxygen and moisture can therefore be suppressed.

Embodiments

Embodiments of the present invention are explained below.

Embodiment 1

A schematic diagram of an element structure of an EL element used inimplementing the present invention is shown in FIG. 2. Reference numeral201 denotes a substrate in FIG. 2, and light transmitting materials suchas glass and quartz can be used for the substrate 201. Further,reference numeral 202 denotes an anode. The anode 202 is formed by ITO,an alloy of tin oxide and indium oxide, but chemical compounds in whichfrom 2 to 20% of zinc oxide (ZnO) is mixed into indium oxide, andchemical compounds made from zinc oxide and calcium oxide may also beused. Furthermore, edge portions of the anode 202 are covered by aninsulating film 214 made from an insulating material.

An EL layer 207 is formed next having a lamination structure made from ahole injecting layer 203, a hole transporting layer 204, a lightemitting layer 205, and a buffer layer 206. Specifically, copperphthalocyanine (Cu-Pc) and PEDOT, which is a polythiophene derivative,can be used in forming the hole injecting layer 203.

Note that the hole injecting layer 203 may be formed by evaporation forcases of using a low molecular weight material such as copperphthalocyanine, and may be formed by spin coating or inkjet printing forcases of using a high molecular weight material such as PEDOT. Further,MTDATA and á-NPD can be used as the hole transporting layer 204.

Next, a known organic EL material can be used as the light emittinglayer 205, and high molecular weight EL materials and low molecularweight EL materials can be used. Note that a case of forming a lightemitting layer composed of three colors, a red color light emittinglayer for displaying red color emitted light, a green color lightemitting layer for displaying green color emitted light, and a bluecolor light emitting layer for displaying blue color emitted light, isexplained in embodiment 1.

The red color light emitting layer can be formed using Alq₃ doped withDCM. In addition, it can also be formed using a material such as an Eucomplex (Eu(DCM)₃(Phen)), or an aluminum quinolinolate complex (Alq₃)doped with DCM-1. Next, the green color light emitting layer can beformed by common evaporation of CPB and Ir(ppy)3. Note that aluminumquinolinolate complex (Alq₃) and benzo-quinolinolate beryllium (BeBq)can also be used. In addition, it is also possible to use a materialsuch as aluminum quinolinolate complex (Alq₃) into which coumarin 6 orquinacridon is doped can be used. The blue color light emitting layercan be formed by using DPVBi, which is a distyrylarylene derivative, azinc complex possessing an azomethine compound in its ligands, or DPVBidoped with perillin.

Furthermore, materials such as lithium fluoride (LiF), aluminum oxide(Al₂O₃), and lithium acetyl acetate can be used as the buffer layer 206.

The lamination structure of the EL layer 207 is thus complete. Note thatthe EL layers may be formed using evaporation if formed using lowmolecular weight materials, and further, may be formed using a processsuch as an application process like spin coating and ink jet printing,or by a process such as printing.

A cathode 208 is formed next on the EL layer 207. Considering thatelectrons are injected from the cathode, it is necessary to use ametallic material having a low work coefficient. However, low workcoefficient metals are unstable in the atmosphere, and oxidation andpeeling become problems. Consequently, it is effective to use an alloy(MgAg) formed by common evaporation of magnesium (Mg) and silver (Ag) ina 9:1 ratio. Further, an alloy of aluminum, lithium or calcium, andmagnesium may also be used. It is also possible to use ytterbium (Yb).

A protective electrode 209 is formed from silver (Ag) in embodiment 1with the aim of lowering the cathode resistance and suppressing cathodeoxidation. Note that it is not always necessary to form the protectiveelectrode, and it need not be formed depending upon the circumstances.

A barrier layer 210 is formed next. The barrier layer 210 is formed inorder to prevent oxygen and moisture absorbed by the absorption layerfrom directly contacting the cathode. Note that it is not alwaysnecessary to form the barrier layer, and it need not be formed if notneeded. Note also that an insulating material, specifically copperphthalocyanine, silicon nitride, or silicon oxide, may be used as thematerial for forming the barrier film.

An absorption film 211 is formed on the barrier film 210. A metal havinga low work coefficient is used as the absorption film 211. This isbecause low work coefficient metals easily oxidize. In addition, a metalin which the oxide produced by the oxidation takes in moisture to becomea hydrate is used here. Specifically, barium (Ba) can be used. Barium isknown to react with oxygen and water as follows:2Ba+O₂2BaOBaO+9H₂OBa(OH)₂.8H₂O

Namely, barium has a function of reacting with and taking in oxygen,moisture and the like existing in the space, according to this chemicalequation. In other words, this chemical behavior is effectively utilizedas a chemical absorption film.

Further, it is preferable to perform film formation of the EL layer 207,the cathode 208, the protective electrode 209, the barrier film 210, andthe absorption film 211 such that oxygen and moisture are not containedin the interfaces between films. It is therefore necessary for the filmsto be formed in succession under a vacuum, or that there is no contactwith oxygen or moisture after forming the EL layer 207 under an inertgas atmosphere, such as that of nitrogen or a noble gas.

It is possible to perform film formation like that stated above with afilm formation apparatus using a multi-chamber method (cluster toolmethod) in embodiment 1.

After thus performing film formation, a sealing substrate 213 is bondedto the substrate 201 using a sealant 212. An ultraviolet setting resinis used in this embodiment as the sealant 212. A region surrounded bythe substrate 201, the sealing substrate 213, and the sealant 212 refersto a space 215.

Materials such as glass, quartz, plastics (including plastic films), andmetallic typically stainless steels) ceramics can be used as the sealingsubstrate. Note that FRP fiberglass reinforced plastics) plate, PVF(polyvinyl fluoride) films, Mylar films, polyester films, and acrylicresin films can be used as plastics.

Evaluation of the state of deterioration of the EL element from the timeof panel manufacture was performed based on the brightness obtainedversus the voltage applied to the EL elements in an EL panel having theabove stated enclosure structure. Note that, although not shown in FIG.2, the cathode and the anode of the EL element are each electricallyconnected to an external electric power source.

Further, the element structure of the EL elements used in evaluation isas shown below. First, an EL layer is formed after forming an anode on aglass substrate by using ITO. The EL layer has a lamination structure asshown below.

After first forming a hole injecting layer by forming copperphthalocyanine with a film thickness of 20 nm,(4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine), hereafterreferred to as MTDATA, is formed with a film thickness of 20 nm and4,4′-bis(N-(1-naphthyl)-N-phenylamino)-biphenyl, hereafter referred toas á-NPD) is formed having a film thickness of 10 nm, as a holetransporting layer. Tris-(8-quinolinolate) aluminum (hereafter referredto as Alq₃) is formed next with a film thickness of 50 nm as a lightemitting layer, and lithium acetyl acetonate (hereafter referred to asLiacac) is formed having a film thickness of 2 nm as a buffer layer. TheEL layer is thus formed.

Mg:Ag is formed next with a 150 nm film thickness as a cathode, and Agis formed with a 150 film thickness on the Mg:Ag film as a protectiveelectrode. A structure in which the EL element is formed up through thispoint is sealed under a nitrogen atmosphere by the glass substrate andan ultraviolet setting resin is referred to as “no Ba”. In addition, astructure sealed under a nitrogen atmosphere by the glass substrate andan ultraviolet setting resin after forming copper phthalocyanine with athickness of 20 nm on the protective electrode as a barrier film, andforming barium having a film thickness of 1500 nm on the barrier film,is referred to as “having Ba”.

Results obtained here are shown in FIG. 3. With the initial propertiesof the manufactured EL element taken as those of the day of manufacture,results measured after exposing the EL element to high temperature, highhumidity conditions of a temperature of 60° C. and 95% humidity for oneday, and measured after exposure for two days, are respectively shown by1-day and 2-day symbols in the figure. Note that the drive voltage hereis set to 7 V.

It can be seen from the results of FIG. 3 that the brightness fallsslightly after one day for the “no Ba” EL element, and has fallen byover 1000 candela after two days. On the other hand, the “having Ba” ELelement shows almost no drop in brightness even after two days.

In addition, photographs of the “no Ba” EL element observed here areshown in FIGS. 11A to 11C, while photographs of the “having Ba” ELelement are shown in FIGS. 12A to 12C. Note that, the state of the ELelements immediately after manufacture are shown in FIGS. 11A and 12A,the states after exposure to high temperature and high humidity for oneday are shown in FIGS. 11B and 12B, and the states after exposure fortwo days are shown in FIGS. 11C and 12C, respectively.

In FIGS. 11A to 11C, a state showing deterioration of the “no Ba” ELelement is already confirmed after one day, while no elementdeterioration can be seen after one day for the “having Ba” EL elementin FIGS. 12A to 12C. After the second day, indications of slightdeterioration can be seen, but it is understood that the EL elementdeterioration for the “having Ba” EL element is slower. The suppressionof EL element deterioration by the formation of an absorption film madefrom barium is thus confirmed.

Embodiment 2

Next, the case of using the present invention to the light-emittingdevice of an active matrix type is explained in this embodiment. Here, amethod of simultaneously manufacturing TFTs (n-channel TFT and p-channelTFT) in a pixel portion and a driver circuit provided in the peripheryof the pixel portion on the same substrate and also manufacturing an ELelement is described in detail with reference to FIG. 4A to FIG. 7.

First, in this embodiment, a substrate 300 is used, which is made ofglass such as barium borosilicate glass or alumino borosilicate glass,typified by #7059 glass or #1737 glass of Corning Inc. There is nolimitation on the substrate 300 as long as a substrate having a lighttransmitting property is used, and a quartz substrate may also be used.In addition, a plastic substrate having heat resistance to a treatmenttemperature of this embodiment may also be used.

Then, a base film 301 formed of an insulating film such as a siliconoxide film, a silicon nitride film or a silicon oxide nitride film isformed on the substrate 300. In this embodiment, a two-layer structureis used for the base film 301. However, a single layer film or alamination structure consisting of two or more layers of the insulatingfilm may also be used. As a first layer of the base film 301, a siliconoxide nitride film 301 a is formed with a thickness of 10 to 200 nm(preferably 50 to 100 nm) using SiH₄, NH₃, and N₂O as reaction gases bya plasma CVD method. In this embodiment, the silicon oxide nitride film301 a (composition ratio Si=32%, O=27%, N=24% and H=17%) having a filmthickness of 50 nm is formed. Then, as a second layer of the base film301, a silicon oxide nitride film 301 b is formed so as to be laminatedon the first layer with a thickness of 50 to 200 nm (preferably 100 to150 nm) using SiH₄ and N₂O as reaction gases by the plasma CVD method.In this embodiment, the silicon oxide nitride film 301 b (compositionratio Si=32%, O=59%, N=7% and H=2%) having a film thickness of 100 nm isformed.

Subsequently, semiconductor layers 302 to 306 are formed on the basefilm. The semiconductor layers 302 to 306 are formed such that asemiconductor film having an amorphous structure is formed by a knownmethod (a sputtering method, an LPCVD method, a plasma CVD method or thelike), and is subjected to a known crystallization process (a lasercrystallization method, a thermal crystallization method, a thermalcrystallization method using a catalyst such as nickel, or the like) toobtain a crystalline semiconductor film, and the crystallinesemiconductor film is patterned into desired shapes. The semiconductorlayers 302 to 306 are formed with a thickness of 25 to 80 nm (preferably30 to 60 nm). The material of the crystalline semiconductor film is notparticularly limited, but it is preferable to form the film usingsilicon, a silicon germanium (Si_(x)Ge_(1-x) (X=0.0001 to 0.02)) alloy,or the like. In this embodiment, an amorphous silicon film of 55 nmthickness is formed by a plasma CVD method, and then, anickel-containing solution is held on the amorphous silicon film. Adehydrogenation process of the amorphous silicon film is performed (at500° C. for 1 hour), and thereafter a thermal crystallization process isperformed (at 550° C. for 4 hours) thereto. Further, to improve thecrystallinity, a laser annealing process is performed to for thecrystalline silicon film. Then, this crystalline silicon film issubjected to a patterning process using a photolithography method toobtain the semiconductor layers 302 to 306.

Further, after the formation of the semiconductor layers 302 to 306, aminute amount of impurity element (boron or phosphorus) may be doped tocontrol a threshold value of the TFT.

Besides, in the case where the crystalline semiconductor film ismanufactured by the laser crystallization method, a pulse oscillationtype or continuous emission type excimer laser, YAG laser, or YVO₄ lasermay be used. In the case where those lasers are used, it is appropriateto use a method in which laser light radiated from a laser oscillator iscondensed into a linear shape by an optical system, and is irradiated tothe semiconductor film. Although the conditions of crystallizationshould be properly selected by an operator, in the case where theexcimer laser is used, a pulse oscillation frequency is set to 300 Hz,and a laser energy density is set to 100 to 400 mJ/cm² (typically 200 to300 mJ/cm²). In the case where the YAG laser is used, it is appropriateto set a pulse oscillation frequency as 30 to 300 Hz using the secondharmonic, and to set a laser energy density to 300 to 600 mJ/cm²(typically, 350 to 500 mJ/cm²). Then, laser light condensed into alinear shape with a width of 100 to 1000 μm, for example, 400 μm, isirradiated to the whole surface of the substrate, and an overlappingratio (overlap ratio) of the linear laser light at this time may be setto 50 to 90%.

A gate insulating film 307 is then formed for covering the semiconductorlayers 302 to 306. The gate insulating film 307 is formed of aninsulating film containing silicon with a thickness of 40 to 150 nm by aplasma CVD or sputtering method. In this embodiment, the gate insulatingfilm 307 is formed of a silicon oxide nitride film with a thickness of110 nm by the plasma CVD method (composition ratio Si=32%, O =59%, N=7%,and H=2%). Of course, the gate insulating film is not limited to thesilicon oxide nitride film, and other insulating films containingsilicon may be used with a single layer or a lamination structure.

Besides, when a silicon oxide film is used, it can be formed such thatTEOS (tetraethyl orthosilicate) and O₂ are mixed by the plasma CVDmethod with a reaction pressure of 40 Pa and a substrate temperature of300 to 400° C., and discharged at a high frequency (13.56 MHz) powerdensity of 0.5 to 0.8 W/cm². The silicon oxide film thus manufacturedcan obtain satisfactory characteristics as the gate insulating film bysubsequent thermal annealing at 400 to 500° C.

Then, as shown in FIG. 4A, a first conductive film 308 of 20 to 100 nmthickness and a second conductive film 309 of 100 to 400 nm thicknessare formed into lamination on the gate insulating film 307. In thisembodiment, the first conductive film 308 made of a TaN film with athickness of 30 nm and the second conductive film 309 made of a W filmwith a thickness of 370 nm are formed into lamination. The TaN film isformed by sputtering with a Ta target under a nitrogen containingatmosphere. Besides, the W film is formed by sputtering with a W target.The W film may also be formed by a thermal CVD method using tungstenhexafluoride (WF₆). Whichever method is used, it is necessary to makethe material have low resistance for use as a gate electrode, and it ispreferred that the resistivity of the W film is set to 20 μΩcm or less.It is possible to make the W film have low resistance by making thecrystal grains large. However, in the case where many impurity elementssuch as oxygen are contained within the W film, crystallization isinhibited and the resistance becomes higher. Therefore, in thisembodiment, the W film is formed by sputtering using a W target having ahigh purity of 99.9999%, and also by taking sufficient consideration soas to prevent impurities within the gas phase from mixing therein duringthe film formation, and thus, a resistivity of 9 to 20 μΩcm can berealized.

Note that, in this embodiment, the first conductive film 308 is made ofTaN, and the second conductive film 309 is made of W, but the materialis not particularly limited thereto, and either film may be formed froman element selected from the group consisting of Ta, W, Ti, Mo, Al, Cu,Cr, and Nd or an alloy material or a compound material containing theabove element as its main constituent. Besides, a semiconductor filmtypified by a polycrystalline silicon film doped with an impurityelement such as phosphorus may be used. An alloy made of Ag, Pd, and Cumay also be used. Further, any combination may be employed such as acombination in which the first conductive film is formed of a tantalum(Ta) film and the second conductive film is formed of a W film, acombination in which the first conductive film is formed of a titaniumnitride (TiN) film and the second conductive film is formed of a W film,a combination in which the first conductive film is formed of a tantalumnitride (TaN) film and the second conductive film is formed of an Alfilm, or a combination in which the first conductive film is formed of atantalum nitride (TaN) film and the second conductive film is formed ofa Cu film.

Next, as shown in FIG. 4B, masks 310 to 314 made of resist are formed byusing a photolithography method, and a first etching process for formingelectrodes and wirings is carried out. In the first etching process,first and second etching conditions are used. In this embodiment, as thefirst etching condition, an ICP (inductively coupled plasma) etchingmethod is used, in which CF₄, Cl₂, and O₂ are used as etching gases, agas flow rate is set to 25/25/10 sccm, and an RF (13.56 MHz) power of500 W is applied to a coil shape electrode under a pressure of 1 Pa togenerate plasma. Thus, the etching is performed. A dry etching deviceusing ICP (Model E645-ICP) manufactured by Matsushita ElectricIndustrial Co. is used here. A 150 W RF (13.56 MHz) power is alsoapplied to the substrate side (sample stage), thereby substantiallyapplying a negative self-bias voltage. The W film is etched under thefirst etching condition, and the end portion of the first conductivelayer is formed into a tapered shape. In the first etching condition,the etching rate for W is 200.39 nm/min, the etching rate for TaN is80.32 nm/min, and the selectivity of W to TaN is about 2.5. Further, thetaper angle of W is about 26° under the first etching condition.

Thereafter, as shown in FIG. 4B, the etching condition is changed intothe second etching condition without removing the masks 310 to 314 madeof resist, and the etching is performed for about 30 seconds, in whichCF₄ and Cl₂ are used as the etching gases, a gas flow rate is set to30/30 sccm, and an RF (13.56 MHz) power of 500 W is applied to a coilshape electrode under a pressure of 1 Pa to generate plasma. An RF(13.56 MHz) power of 20 W is also applied to the substrate side (samplestage), and a substantially negative self-bias voltage is appliedthereto. In the second etching condition in which CF₄ and Cl₂ are mixed,the W film and the TaN film are etched to the same degree. In the secondetching condition, the etching rate for W is 58.97 nm/min, and theetching rate for TaN is 66.43 nm/min. Note that, in order to perform theetching without leaving any residue on the gate insulating film, it isappropriate that an etching time is increased by approximately 10 to20%.

In the above first etching process, by making the shapes of the masksformed of resist suitable, end portions of the first conductive layerand the second conductive layer become tapered shape by the effect ofthe bias voltage applied to the substrate side. The angle of the taperportion may be 15 to 45°. In this way, first shape conductive layers 315to 319 consisting of the first conductive layer and the secondconductive layer (first conductive layers 315 a to 319 a and secondconductive layers 315 b to 319 b) are formed by the first etchingprocess. Reference numeral 320 indicates a gate insulating film, and theregions not covered with the first shape conductive layers 315 to 319are made thinner by approximately 20 to 50 nm by etching.

Then, a first doping process is performed to add an impurity elementimparting n-type conductivity to the semiconductor layer withoutremoving the masks made of resist (FIG. 4B). Doping may be carried outby an ion doping method or an ion injecting method. The condition of theion doping method is that a dosage is 1×10¹³ to 5×10¹⁵ atoms/cm², and anacceleration voltage is 60 to 100 keV. In this embodiment, the dosage is1.5×10¹⁵ atoms/cm² and the acceleration voltage is 80 keV. As theimpurity element imparting n-type conductivity, an element belonging togroup 15 of the periodic table, typically phosphorus (P) or arsenic (As)is used, but phosphorus (P) is used here. In this case, the conductivelayers 315 to 319 become masks for the impurity element imparting n-typeconductivity, and high concentration impurity regions 321 to 325 areformed in a self-aligning manner. The impurity element imparting n-typeconductivity in a concentration range of 1×10²⁰ to 1×10²¹ atoms/cm³ isadded to the high concentration impurity regions 321 to 325.

Thereafter, as shown in FIG. 4C, a second etching process is performedwithout removing the masks made of resist. Here, a gas mixture of CF₄,Cl₂ and O₂ is used as an etching gas, the gas flow rate is set to20/20/20 sccm, and a 500 W RF (13.56 MHz) power is applied to a coilshape electrode under a pressure of 1 Pa to generate plasma, therebyperforming etching. A 20 W RF (13.56 MHz) power is also applied to thesubstrate side (sample stage), thereby substantially applying a negativeself-bias voltage. In the second etching process, the etching rate for Wis 124.62 nm/min, the etching rate for TaN is 20.67 nm/min, and theselectivity of W to TaN is 6.05. Accordingly, the W film is selectivelyetched. The taper angle of W is 70° by the second etching process.Second conductive layers 330 b to 334 b are formed by the second etchingprocess. On the other hand, the first conductive layers 315 a to 319 aare hardly etched, and first conductive layers 330 a to 334 a areformed.

Next, a second doping process is performed. The second conductive layers330 b to 334 b are used as masks for an impurity element, and doping isperformed such that the impurity element is added to the semiconductorlayer below the tapered portions of the first conductive layers. In thisembodiment, phosphorus (P) is used as the impurity element, and plasmadoping is performed with a dosage of 1.5×10¹⁴ atoms/cm², a currentdensity of 0.5 μA, and an acceleration voltage of 90 keV. Thus, lowconcentration impurity regions 340 to 344, which overlap with the firstconductive layers, are formed in self-aligning manner. The concentrationof phosphorus (P) added to the low concentration impurity regions 340 to344 is 1×10¹⁷ to 5×10¹⁸ atoms/cm³, and has a gentle concentrationgradient in accordance with the film thickness of the tapered portionsof the first conductive layers. Note that in the semiconductor layersthat overlap with the tapered portions of the first conductive layers,the concentration of the impurity element slightly falls from the endportions of the tapered portions of the first conductive layers towardthe inner portions, but the concentration keeps almost the same level.Further, an impurity element is added to the high concentration impurityregions 321 to 325 to form high concentration impurity regions 345 to349.

Thereafter, as shown in FIG. 5B, after the masks made of resist areremoved, a third etching process is performed using a photolithographymethod. The tapered portions of the first conductive layers arepartially etched so as to have shapes overlapping the second conductivelayers in the third etching process. Incidentally, as shown in FIG. 5B,masks made of resist (350, 351) are formed in the regions where thethird etching process is not conducted.

The etching condition in the third etching process is that Cl₂ and SF₆are used as etching gases, the gas flow rate is set to 10/50 sccm, andthe ICP etching method is used as in the first and second etchingprocesses. Note that, in the third etching process, the etching rate forTaN is 111.2 nm/min, and the etching rate for the gate insulating filmis 12.8 nm/min.

In this embodiment, a 500 W RF (13.56 MHz) power is applied to a coilshape electrode under a pressure of 1.3 Pa to generate plasma, therebyperforming etching. A 10 W RF (13.56 MHz) power is also applied to thesubstrate side (sample stage), thereby substantially applying a negativeself-bias voltage. Thus, first conductive layers 352 a to 354 a areformed.

Impurity regions (LDD regions) 355 to 357, which do not overlap thefirst conductive layers 352 a to 354 a, are formed by theabove-mentioned third etching process. Note that impurity regions (GOLDregions) 340 and 342 remains overlapping the first conductive layers 330a and 332 a.

Further, the electrode constituted of the first conductive layer 330 aand the second conductive layer 330 b finally becomes the gate electrodeof the n-channel TFT of the driver circuit, and the electrodeconstituted of the first conductive layer 352 a and a second conductivelayer 352 b finally becomes the gate electrode of the p-channel TFT ofthe driver circuit.

Similarly, the electrode constituted of the first conductive layer 353 aand a second conductive layer 353 b finally becomes the gate electrodeof the n-channel TFT of the pixel portion, and the electrode constitutedof the first conductive layer 354 a and a second conductive layer 354 bfinally becomes the gate electrode of the p-channel TFT of the pixelportion. Further, the electrode constituted of the first conductivelayer 332 a and the second conductive layer 332 b finally becomes one ofelectrodes of a capacitor (storage capacitor) of the pixel portion.

In this way, in this embodiment, the impurity regions (LDD regions) 355to 357 that do not overlap the first conductive layers 352 a to 354 aand the impurity regions (GOLD regions) 340 and 342 that overlap thefirst conductive layers 330 a and 332 a can be simultaneously formed.Thus, different impurity regions can be formed in accordance with theTFT characteristics.

Next, after the masks 350 and 351 made of resist are removed, the gateinsulating film 320 is subjected to an etching process. In this etchingprocess, CHF₃ is used as an etching gas, and a reactive ion etchingmethod (RIE method) is used. In this embodiment, a fourth etchingprocess is conducted with a chamber pressure of 6.7 Pa, RF power of 800W, and a gas flow rate of CHF₃ of 35 sccm. Thus, parts of the highconcentration impurity regions 345 to 349 are exposed, and insulatingfilms 360 to 364 are formed.

Subsequently, masks 365 and 366 made of resist are newly formed tothereby perform a third doping process. By this third doping process,impurity regions 370 to 375 added with an impurity element impartingconductivity (p-type) opposite to the above conductivity (n-type) areformed in the semiconductor layers that become active layers of thep-channel TFT (FIG. 5C). The first conductive layers 352 a, 332 a, and354 a are used as masks for the impurity element, and the impurityelement imparting p-type conductivity is added to form the impurityregions in a self-aligning manner.

In this embodiment, the impurity regions 370 to 375 are formed by an iondoping method using diborane (B₂H₆). The impurity regions 370 to 375 arerespectively added with phosphorous at different concentrations by thefirst doping process and the second doping process. In any of theregions, the doping process is conducted such that the concentration ofthe impurity element imparting p-type conductivity becomes 2×10²⁰ to2×10²¹ atoms/cm³. Thus, the impurity regions function as source anddrain regions of the p-channel TFT, and therefore, no problem occurs.

Through the above-described processes, the impurity regions are formedin the respective semiconductor layers. Note that, in this embodiment, amethod of conducting doping of the impurities (boron) after etching thegate insulating film is shown, but doping of the impurities may beconducted before etching the gate insulating film and without theetching of the gate insulating film.

Subsequently, the masks 365 and 366 made of resist are removed, and asshown in FIG. 6A, a first interlayer insulating film 376 is formed. Asthe first interlayer insulating film 376, an insulating film containingsilicon is formed with a thickness of 100 to 200 nm by a plasma CVDmethod or a sputtering method. In this embodiment, a silicon oxidenitride film of 150 nm thickness is formed by the plasma CVD method. Ofcourse, the first interlayer insulating film 376 is not limited to thesilicon oxide nitride film, and other insulating films containingsilicon may be used in a single layer or a lamination structure.

Then, a process of activating the impurity element added to thesemiconductor layers is performed. This activation process is performedby a thermal annealing method using an annealing furnace. The thermalannealing method may be performed in a nitrogen atmosphere with anoxygen concentration of 1 ppm or less, preferably 0.1 ppm or less and at400 to 700° C., typically 500 to 550° C. In this embodiment, theactivation process is conducted by a heat treatment for 4 hours at 550°C. Note that, in addition to the thermal annealing method, a laserannealing method or a rapid thermal annealing method (RTA method) can beapplied:

Note that, in this embodiment, with the above-mentioned activationprocess, nickel used as a catalyst in crystallization is gettered to theimpurity regions (345, 348, 370, 372 and 374) containing phosphorous athigh concentration, and the nickel concentration in the semiconductorlayer that becomes a channel forming region is mainly reduced. The TFTthus manufactured having the channel forming region has the lowered offcurrent value and good crystallinity to obtain a high electric fieldeffect mobility. Thus, the satisfactory characteristics can be attained.

Further, the activation process may be conducted before the formation ofthe first interlayer insulating film. Incidentally, in the case wherethe used wiring material is weak to heat, the activation process ispreferably conducted after the formation of the interlayer insulatingfilm (insulating film containing silicon as its main constituent, forexample, silicon nitride film) in order to protect wirings and the likeas in this embodiment.

Furthermore, after the activation process, the doping process isperformed, thus the first interlayer insulating film may be formed.

Moreover, a heat treatment is carried out at 300 to 550° C. for 1 to 12hours in an atmosphere containing hydrogen of 3 to 100% to perform aprocess of hydrogenating the semiconductor layers. In this embodiment,the heat treatment is conducted at 410° C. for 1 hour in a nitrogenatmosphere containing hydrogen of approximately 3%. This is a process ofterminating dangling bonds in the semiconductor layer by hydrogenincluded in the interlayer insulating film. As another means forhydrogenation, plasma hydrogenation (using hydrogen excited by plasma)may be performed.

In addition, in the case where the laser annealing method is used as theactivation process, after the hydrogenation process, laser light emittedfrom an excimer laser, a YAG laser or the like is desirably irradiated.

Next, as shown in FIG. 6B, a second interlayer insulating film 380,which is made from an organic insulating material, is formed on thefirst interlayer insulating film 376. In this embodiment, an acrylicresin film is formed with a thickness of 1.6 μm. Then, patterning forforming contact holes that reach the respective impurity regions 345,348, 370, 372 and 374 is conducted.

As the second interlayer insulating film 380, a film made from aninsulating material containing silicon or an organic resin is used. Asthe insulating material containing silicon,-silicon oxide, siliconnitride, or silicon oxide nitride may be used. As the organic resin,polyimide, polyamide, acrylic, BCB (benzocyclobutene), or the like maybe used.

In this embodiment, the silicon oxide nitride film formed by a plasmaCVD method is formed. Note that the thickness of the silicon oxidenitride film is preferably 1 to 5 μm (more preferably 2 to 4 μm). Thesilicon oxide nitride film has a little amount of moisture contained inthe film itself, and thus, is effective in suppressing deterioration ofthe EL element.

Further, dry etching or wet etching may be used for the formation of thecontact holes. However, taking the problem of electrostatic destructionin etching into consideration, the wet etching method is desirably used.

Moreover, in the formation of the contact holes here, the firstinterlayer insulating film 376 and the second interlayer insulating film380 are etched at the same time. Thus, in consideration for the shape ofthe contact hole, it is preferable that the material with an etchingspeed faster than that of the material for forming the first interlayerinsulating film 376 is used for the material for forming the secondinterlayer insulating film 380.

Then, wirings 381 to 388, which are electrically connected with theimpurity regions 345, 348, 370, 372 and 374, respectively, are formed.The wirings are formed by patterning a lamination film of a Ti film of50 nm thickness and an alloy film (alloy film of Al and Ti) of 500 nmthickness, but other conductive films may also be used.

Subsequently, a transparent conductive film is formed thereon with athickness of 80 to 120 nm, and by patterning the transparent conductivefilm, a pixel electrode 389 is formed (FIG. 6B).

Note that, in this embodiment, an indium tin oxide (ITO) film or atransparent conductive film in which indium oxide is mixed with zincoxide (ZnO) of 2 to 20% is used as the transparent electrode.

Further, the pixel electrode 389 is electrically connected to the drainregion of the electric current control TFT by forming the pixelelectrode 389 so as to contact and overlap with the drain wiring 387.

Next, as shown in FIG. 7, an insulating film containing silicon (asilicon oxide film in embodiment 2) is formed with a thickness of 500nm, an opening portion is formed in a position corresponding to thepixel electrode 389, and a third interlayer insulating film 390 whichfunctions as a bank is formed. A taper shape sidewall can easily be madeby using wet etching when forming the opening portion. If the sidewallof the opening portion is not sufficiently gentle, then deterioration ofthe EL layer due to a step becomes a problem, and therefore it isnecessary to use care here.

Note that, although a film made from silicon oxide is used as the thirdinterlayer insulating film 390 in embodiment 2, organic resin films suchas those formed from polyimide, polyamide, acrylic, and BCB(benzocyclobutene) can also be used, depending upon the circumstances.

An EL layer 391 is formed next by evaporation, as shown in FIG. 7. Oneexample of the EL layer 391 formed according to the present invention isshown here.

After first forming copper phthalocyanine (hereafter referred to asCu-Pc) on the pixel electrode (anode) 389 with a film thickness of 20 nmas a hole injecting layer, MTDATA is formed having a film thickness of20 nm, and á-NPD is formed having a film thickness of 10 nm, as a holetransporting layer. Alq₃ is formed next with a film thickness of 50 nmas a light emitting layer, and a 2 nm thickness of Liacac is formed as abuffer layer. The EL layer 391 is thus formed.

Note that known materials can also be used as the materials for formingthe EL layer 391. A four layer structure composed of a hole injectinglayer, a hole transporting layer, a light emitting layer, and anelectron transporting layer is made in embodiment 2, but an electroninjecting layer can also be formed, and it is also possible to omit anyof these layers except the light emitting layer. Various examples ofthis type of combination have already been reported upon, and any suchcombinations may be used.

A cathode (Mg:Ag electrode) 392 and a protective electrode 394 areformed next by evaporation. It is preferable to perform heat treatmentin advance on the pixel electrode 380 before forming the EL layer 391and the cathode 392, thereby completely removing moisture. Note that,although an Mg:Ag electrode is used as the cathode of the EL element inembodiment 2, other known materials may also be used.

Further, the protective electrode 394 is formed to prevent deteriorationof the cathode 392, and to lower the film resistance of the cathode, andmetallic films having low resistance with aluminum as the mainconstituent are typical. Other materials may also be used, of course.Further, it is not always necessary to form the metallic film, and itneed not be formed when not necessary.

In addition, a barrier film 395 is formed. The barrier film is formed inorder to prevent direct contact of oxygen and moisture, captured by anabsorption film formed subsequently, with the cathode and the protectiveelectrode. Note that an insulating film made from Cu-Oc is used as thebarrier film in embodiment 2.

The film thickness of the EL layer 391 may be set from 10 to 400 nm(typically between 60 and 150 nm), and the film thickness of the cathode392 may be set from 80 to 200 nm (typically between 100 and 150 nm).

An absorption film 396 is formed next so as to cover the EL element 393,the protective electrode 394, and the barrier film 395. It is preferableto use a metal having a low work coefficient and possessing absorptionproperties as the absorption film 396, and barium is used in embodiment2. Note that the film thickness of the absorption film 396 maybe setfrom 1 to 3 ìm (typically between 1.5 and 2 ìm).

The EL element 393 is weak with respect to oxygen and moisture, andtherefore it is preferable to perform processing in succession from theformation of the EL layer 391 to the formation of the absorption film396.

In addition, a structure is used in embodiment 2 in which a passivationfilm 397, composed of an insulating film such as a nitride film or anoxide film, is formed on the absorption film 396 in order to increasethe adhesion of a sealant prepared between the sealing substrate and thesubstrate during sealing. However, it is not always necessary to formthe passivation film 397, and it may be formed only when needed.

The structure shown in FIG. 7 is thus complete. A structure manufacturedup through that shown in FIG. 7 is referred to as an EL substrate withinthis specification.

Note that there is emission from the lower surface with the elementstructure of the EL element 393, and therefore a structure is shown inwhich an n-channel TFT is used as a switching TFT 503, and a p-channelTFT is used as an electric current control TFT 504. However, this isonly a preferred structure in embodiment 2, and there are no limitationsplaced upon the structure.

Note that the driver voltage of the TFTs used in embodiment 2 is from1.2 to 10 V, preferably between 2.5 and 5.5 V.

A method for sealing the EL substrate shown in FIG. 7 by using a sealingsubstrate and completing an EL panel is explained next using FIGS. 8Aand 8B.

FIG. 8A is an upper surface diagram of an EL panel having a sealed ELsubstrate, and FIG. 8B is a cross sectional diagram of FIG. 8A cut alongthe line A-A′. Reference numeral 801 shown by a dotted line denotes asource side driver circuit, reference numeral 802 denotes a pixelportion, and reference numeral 803 denotes a gate side driver circuit.Further, reference numeral 804 denotes a sealing substrate, referencenumeral 805 denotes a sealing material, and the inside portionsurrounded by he sealing material 805 is a space 807.

Note that video signals and clock signals are received from an externalinput terminal FPC (flexible printed circuit) through a wiring (notshown in the figures) for transmitting input signals to the source sidedriver circuit 801 and to the gate side driver circuit 803. Note alsothat, although a state in which an FPC is connected to the EL panel isshown, a module in which an IC (integrated circuit) is directly mountedthrough an FPC is referred to as a light emitting device within thisspecification.

The cross sectional structure is explained next using FIG. 8B. The pixelportion 802 and the gate side driver circuit 803 are formed above asubstrate 810, and the pixel portion 802 is formed by a plurality ofpixels including electric current control TFTs 811 and pixel electrodes812 that are electrically connected to drains of the electric currentcontrol TFTs 811. Further, the gate side driver circuit is formed usingCMOS circuits (refer to FIG. 7) in which n-channel TFTs 813 andp-channel TFTs 814 are combined.

The pixel electrode 812 functions as an anode. Furthermore, afterforming banks 815 in both edges of the pixel electrode 812, an EL layer816 and a cathode 817 are formed on the pixel electrode 812, forming anEL element 818.

Note that the cathode 817 functions as a common wiring for all pixels,and is electrically connected to the FPC 809 via a connection wiring808.

A barrier film 819 and an absorption film 820 are formed next insuccession so as to cover the EL element 818. Note that the barrier film819 formed here is formed in order to avoid oxygen and moisture absorbedby the absorption film 820 coming into direct contact with the cathode817. In addition, it is also formed in order to prevent direct contactpressure from being applied to the EL element 818 by weight developingby oxygen and moisture absorbed by the absorption film 820. It istherefore preferable to use an insulating material as the material forforming the barrier film 819, and silicon nitride and silicon oxidematerials are suitable.

A metal having a low work coefficient is used as the absorption film820. This is because low work coefficient metals easily oxidize. Inaddition, a metal in which the oxide produced by the oxidation takes inmoisture to become a hydrate is used here. Specifically, barium (Ba) canbe used.

A passivation film 821 is formed after forming the absorption film 820.The passivation film 821 is formed in order to prevent direct contactbetween the sealant 805 and the connection wiring 808. The adhesivenessof the sealant 805 can be increased by the passivation film 821.

Note that the sealing substrate 804 made from glass is bonded by thesealant 805. It is preferable to use an ultraviolet setting resin or athermosetting resin as the sealant 805. Further, spacers made from aresin film may also be formed when necessary in order to maintain a gapbetween the sealing substrate 804 and the EL element 818. An inert gassuch as nitrogen or a noble gas fills the space 807 on the inside of thesealant 805. Furthermore, it is preferable that the sealant 805 be amaterial which is impermeable to moisture and oxygen.

The EL elements can thus be completely shut off from the outside bysealing the EL elements in the space 807 with a structure like thatdiscussed above, and EL element deterioration due to moisture and oxygenentering from the outside can be prevented. A light emitting devicehaving high reliability can therefore be obtained.

Note that it is possible to implement the constitution of thisembodiment by freely combining it with the constitution of embodiment 1.

Embodiment 3

A case of using the present invention in a passive matrix (simplematrix) light emitting device is explained in this embodiment. FIG. 9 isused in the explanation. Reference numeral 1001 denotes a substrate madefrom glass in FIG. 9, and reference numeral 1002 denotes an anode madefrom a transparent conductive film. A chemical compound of indium oxideand zinc oxide is formed by sputtering as an anode 1002 in embodiment 3.Note that, although not shown in FIG. 9, a plurality of the anodes 1002are arranged in a direction parallel to the page. In addition, banks1003 are formed so as to be buried between the anodes 1002.

Cathodes 1006 arranged in a stripe shape are formed in a verticaldirection to the page.

EL layers 1004 a to 1004 c composed of EL materials are formed next byevaporation, as shown by embodiment 1. Note that the EL layer 1004 a isa red color light emitting EL layer, the EL layer 1004 b is a greencolor light emitting layer, and the EL layer 1004 c is a blue colorlight emitting layer. Organic EL materials used here may be similar tothose of embodiment 1. The EL layers are formed following the grovesformed by the banks 1003, and are thus formed in a form of stripes in avertical direction with respect to the page.

Three colors of pixels, red, green, and blue, are formed in a form ofstripes on the substrate by implementing this embodiment. Note that itis not always necessary to have three colors for the pixels, and onecolor or two colors may also be used. Further, the colors are notlimited to red, green, and blue. Other colors capable of being emitted,such as yellow, orange, and gray, may also be used.

As a method of forming the EL layers, only the red color light emittingEL layer is formed first using a metal mask. After then shifting themetal mask and moving it to the adjacent pixel row, the green colorlight emitting EL layer is formed. In addition, the blue color lightemitting EL layer is formed after moving the metal mask to the adjacentpixel row. EL layers made from red, green, and blue in a form of stripesare thus formed.

Note that the same color light emitting layers may be formed one line ata time, and may also be formed at the same time.

It is preferable that the mutual distance (D) between pixels of the samecolor that are adjacent to each other on a line be equal to or greaterthan 5 times the film thickness (t) of the EL layers (more preferablyequal to or greater than 10 times). This is because the problem of crosstalk occurs when D<5 t. Note that high definition images cannot beobtained if the distance (D) is too large, and therefore 5 t<D<50 t(more preferably, 10 t<D<35 t) is preferable.

The banks may be formed in a form of stripes in a horizontal directionwith respect to the page, and the red color light emitting EL layers,the green color light emitting EL layers, and the blue color lightemitting EL layers may also be formed in the same horizontal direction,respectively.

In this case it is preferable that the mutual distance (D) betweenpixels of the same color that are adjacent to each other on a line beequal to or greater than 5 times the film thickness (t) of the EL layers(more preferably equal to or greater than 10 times), and morepreferably, 5 t<D<50 t (preferably, 10 t<D<35 t).

It becomes possible to control the film formation position by formingthe EL layers using the metal mask, as above.

Next, although not shown in FIG. 9, a plurality of cathode electrodesand the protective electrodes have their longitudinal direction in avertical direction to the page, and are arranged in a stripe shape suchthat they intersect with the anode 1002. Note that the cathodes 1005 aremade from MgAg in this embodiment, and the protective electrodes 1006are made from an aluminum alloy film. Both are formed by evaporation.Further, although not shown in the figure, the protective electrodes1006 have wirings drawn out to a portion at which an FPC is latterattached so that a predetermined voltage can be applied thereto.

EL elements are thus formed on the substrate 1001. The lower sideelectrodes are transparent electrodes in this embodiment, and thereforelight emitted by the EL layers 1004 a to 1004 c is irradiated to thelower surface (substrate 1001). However, the EL element structure can bereversed, and the lower side electrode can be made into a lightshielding cathode. In this case, light emitted by the EL layers 1004 ato 1004 c is irradiated to the upper surface (side opposite thesubstrate 1001).

After forming the protective electrodes 1006, a barrier film 1307 isformed from an insulating material. The inorganic materials such assilicon nitride, silicon oxide, and carbon (specifically a DLC film) canbe used, and the barrier film can be formed by CVD, sputtering, orevaporation. A silicon nitride film is formed by evaporation in thisembodiment. Note that it is preferable that the film thickness of thebarrier film 1007 be from 10 to 100 nm.

Next, an absorption film 1008 made from an absorption material is formedby evaporation. Note that a material having a small work coefficient andwhich easily oxidizes, such as barium, may be used as the absorptionmaterial here.

A passivation film 1009 composed of an insulating material is thenformed on the absorption film 1008. Note that the EL element is weakwith respect to oxygen, moisture, and the-like, and therefore it ispreferable to perform film formation in succession from the EL layer tothe passivation film.

A passive light emitting device having an attached FPC 1013 is thuscomplete.

Note that it is possible to implement the constitution of thisembodiment by freely combining it with any of embodiments 1 and 2.

Embodiment 4

A method for preventing the incursion of contaminants from the outsidesuch as oxygen and moisture after forming an enclosure structure of anEL element is explained in embodiment 4.

A cross sectional diagram of the inside of a film formation chamber 1109for evaporating metallic films on EL panels having enclosure structuresis shown simply in FIG. 10A. Note that the film formation chamber 1109is in a state filled with an inert gas at atmospheric pressure.

Reference numeral 1101 denotes a substrate in FIG. 10A, and EL elements1102 are formed on the substrate. An absorption film 1104 is formed soas to cover the EL elements 1102. A passivation film 1105 is formed onconnection wirings 1103 from the EL elements 1102, and on the absorptionfilm, and these are sealed by a sealing substrate 1108 and a sealant1106. A region sealed the passivation film 1105 and the sealingsubstrate 1108 is a space 1107. The state formed up through this pointis referred to as an EL panel within this specification.

Insertion and extraction of the EL panel is performed through a gate1110 of the film formation chamber 1109. The side of the substrate onwhich the EL elements are formed is then faced toward the bottom, andthe substrate is placed on a support stand 1111 through a mask 1118.

A low melting point metal for forming a metallic film is prepared as anevaporation source 1112 in the film formation chamber 1109. This is inconsideration of damage of the sealant 1106 used in sealing due to heatduring film formation. Specifically, it is preferable to use aluminum ormagnesium.

Evaporation is then performed under atmospheric pressure. Note that amask 1118 is formed when performing the film formation so as not to formthe metallic film on the connection wirings 1103 covered by thepassivation film 1105, or in other unnecessary areas. Further, theposition of the evaporation source 1112 may be moved, and the positionand the angle of the EL panel may be changed, in order to regulate theevaporation location.

As shown in FIG. 10B, portions of the EL panel sealed by the sealant inthis embodiment can be formed so as to be covered by the metallic film1116. Further, reference numeral 1113, 1114, 1115, and 1117 denote ananode, an EL layer, a cathode, and an insulater.

Further, the metallic film can be formed under atmospheric pressure inthis embodiment, and therefore problems associated with pressure changesinside the enclosure structure when the EL panel is removed to theatmosphere after film formation can be prevented.

Note that it is possible to implement the constitution of thisembodiment by freely combining it with the constitution of any ofembodiments 1 to 3.

Embodiment 5

An example of a film formation apparatus used when performing filmformation, sealing processing and the like, from the formation of an ELlayer to the formation of an enclosure structure in each of the aboveembodiments, is shown in this embodiment.

A thin film formation apparatus of the present invention is explainedusing FIG. 13. Reference numeral 1401 denotes a load chamber forperforming entry and removal of a substrate, and the load chamber isalso referred to as a load lock chamber. A carrier 1402 on which asubstrate is set is located here. Note that the load chamber 1401 mayalso be segregated by substrate entry and substrate removal. A substratein a state in which processing up through the formation of EL elementanodes on the substrate is complete is set on the carrier in thisembodiment.

Further, reference numeral 1403 denotes a conveyor chamber (A)containing a mechanism 1405 for conveying the substrate 1404 (alsoreferred to as a conveyor mechanism (A)). One type of conveyor mechanism(A) 1405 is a robot arm for performing handling of a substrate.

A plurality of film formation chambers, processing chambers, and thelike are connected to the conveyor chamber (A) 1403 through gates. Eachof the film formation chambers, the conveyor chamber, and the processingchambers are completely cutoff from each other by the gates. Airtightsealed spaces are thus formed in each of these chambers. Note that theconveyor chamber (A) 1403 is under reduced pressure, and therefore anevacuation pump (not shown in the figure) is prepared in each of theprocessing chambers directly connected to the conveyor chamber (A) 1403.

It is possible to use a rotary oil pump, a mechanical booster pump, aturbo molecular pump, and a cryo pump as the evacuation pump, but a cryopump effective in removing moisture is preferable.

A film formation chamber (A) denoted by reference numeral 1407 isexplained first. The film formation chamber (A) 1407 is connected to theconveyor chamber (A) 1403 by a gate 1406 b, and is a film formationchamber for performing film formation by evaporation. Note that a methodutilizing resistivity evaporation by resistive heating (RE method), anda method utilizing electron beam (EB method) can be used as theevaporation method, and a case of performing evaporation by an RE methodis explained in this embodiment.

Note that a hole injecting layer, a hole transporting layer, a lightemitting layer, an electron transporting layer, and an electroninjecting layer, all for forming an EL layer, are formed in the filmformation chamber (A) 1407.

EL materials used in film formation are prepared in advance in a sampleboat within the film formation chamber (A), and evaporation occurs byheat developing by the application of a voltage to the test piece boat.Note that EL materials are extremely weak with respect to moisture, andtherefore it is necessary always maintain the pressure of the filmformation chamber (A) 1407 in a vacuum state during an EL layerformation. Other than during the insertion and extraction of substratesto/from the film formation chamber (A) 1407, the film formation chamber(A) 1407 may be controlled so that it is normally completely cutoff fromthe conveyor chamber (A) 1405 by means of the gate 1406 b, and there isa vacuum state within the film formation chamber. Note that the filmformation pressure at this time must be set from 1×10⁻⁶ to 1×10⁻⁵ Torr.

Further, a window may also be attached to the side surfaces of the filmformation chamber (A) 1407 as means of observing EL material filmformation from outside of the apparatus. Thus it can be confirmedthrough the window whether film formation is conducted properly. Aplurality of sample boats (not shown in the figure) in which ELmaterials are prepared are formed in the film formation chamber (A)1407, so that a plurality of layers for forming the EL layer can beformed. Specifically, it is preferable to form between one and eighttypes of sample boats.

Films containing EL materials are formed by application of EL solutionscontaining EL materials onto a substrate in a film formation chamber (B)1410 provided with a spin coater for cases of the EL layer formationusing a spin coating method. Note that film formation is performed inthe film formation chamber (B) 1410 when forming films of high molecularweight EL materials. However, depending upon the circumstances, filmformation may also be performed in the film formation chamber (B) 1410for cases in which a low molecular weight EL material is dissolved in asolvent.

Note that the film formation chamber (B) 1410 provided with the spincoater is connected to a conveyor chamber (B) 1414 through a gate 1406g. Note also that a substrate which has undergone film formationprocessing in the film formation chamber (B) 1410 is then conveyed to afiring chamber 1411 by a conveyor mechanism (B) 1409 through a gate 1406h, and firing is performed.

After firing processing is complete, the substrate is conveyed to apressure regulation chamber 1408 connected to the conveyor chamber (B)1414 through a gate 1406 f. The gate 1406 f is closed after thesubstrate is conveyed to the pressure regulation chamber 1408, and theinside of the pressure regulation chamber 1408 becomes a low pressurestate.

When the inside of the pressure regulation chamber 1408 is under a stateof constant low pressure or below, a gate 1406 d is opened, and thesubstrate is extracted by the conveyor mechanism (A) 1405.

The substrate is conveyed to a film formation chamber (C) 1412 connectedto the conveyor chamber (A) 1403 through a gate 1406 c after the ELlayers have been formed. The film formation chamber (C) is a filmformation chamber for performing film formation by evaporation. Notethat evaporation is performed by an RE method, similar to the filmformation chamber (A) 1407 for forming the EL layers in this embodiment.Insulating films such as a barrier film, an absorption film, and apassivation film to be formed over the EL layer are then formed byevaporation in the film formation chamber (C) 1412.

A plurality of substrate boats (not shown in the figure) are also formedin the film formation chamber (C) 1412. Specifically, the insulatingmaterials such as silicon nitride and silicon oxide, which are materialsfor forming a barrier film and a passivation film, and the filmformation material such as barium for forming an absorption film, areprepared.

The substrate is conveyed to a sealing chamber 1413 connected to theconveyor chamber (A) 1403 through a gate 1406 e when film formation upthrough the passivation film is complete. Note that final processing inorder to tightly seal the EL element is performed in the sealing chamber1413. Specifically, sealing of EL elements formed on the substrate byusing a sealing substrate and a sealant is performed.

Materials such as glass, ceramics, and metals can be used as the sealingsubstrate, and thermosetting resins, ultraviolet setting resins, and thelike can be used as the sealant.

Note that a function for performing heat treatment or ultraviolet lightirradiation processing is provided to the sealing chamber 1413.

After sealing processing is performed in the sealing chamber 1413, thesubstrate is once again returned to the load chamber 1401 by theconveyor mechanism (A) 1405 through a gate 1406 a.

Note that it is possible to implement the constitution of thisembodiment by freely combining it with any of embodiments 1 to 4.

Embodiment 6

The light emitting device formed by implementing the present inventionmay be used as a display portion of various electrical appliances andthe pixel portion may be used as an image display portion. As electricalappliances of this invention, there are such as a video camera, adigital camera, a goggle type display (head mounted display), anavigation system, an audio apparatus, a note type personal computer, agame apparatus, a portable apparatus (such as a mobile computer, aportable telephone, a portable game apparatus or an electronic book),and an image play back device equipped with a recording medium. Specificexamples of the electronic appliances are shown in FIGS. 14A to 14F and15A to 15F.

FIG. 14A shows an EL display and includes a casing 2001, a supportingbase 2002 and a display portion 2003. The light emitting device of thisinvention may be used for the display portion 2003. When using the lightemitting device having the EL element in the display portion 2003, sincethe EL element is a self light emitting type, a backlight is notnecessary and the display portion may be made thin.

FIG. 14B shows a video camera, which contains a main body 2101, adisplay portion 2102, a sound input portion 2103, operation switches2104, a battery 2105, and an image receiving portion 2106. The lightemitting device of this invention can be applied to the display portion2102.

FIG. 14C shows a digital camera, which contains a main body 2201, adisplay portion 2202, an eye contact portion 2203, and operationswitches 2204. The light emitting device of this invention can beapplied to the display portion 2202.

FIG. 14D shows an image playback device equipped with a recording medium(specifically, a DVD playback device), which contains a main body 2301,a recording medium (such as a CD, LD or DVD) 2302, operation switches2303, a display portion (a) 2304, a display portion (b) 2305 and thelike. The display portion (a) is mainly used for displaying imageinformation. The display portion (b) 2305 is mainly used for displayingcharacter information. The light emitting device of this invention canbe applied to the display portion (a) and the display portion (b). Notethat the image playback device equipped with the recording medium mayinclude devices such as a CD playback device and the game apparatus.

FIG. 14E shows a portable (mobile) computer, which contains a main body2401, a display portion 2402, an image receiving portion 2403, operationswitches 2404 and a memory slot 2405. The light emitting device of thisinvention can be applied to the display portion 2402. This portablecomputer may record information to a recording medium that hasaccumulated flash memory or involatile memory, and playback suchinformation.

FIG. 14F shows a personal computer, which contains a main body 2501, acasing 2502, a display portion 2503, and a keyboard 2504. The lightemitting device of this invention can be applied to the display portion2503.

The above electronic appliances more often display information sentthrough electron communication circuits such as Internet or the CATV(cable television), and especially an opportunity of an imageinformation display is increasing. When using the light emitting devicehaving the EL element in the display portion, since the response speedof the EL element is extremely fast, it becomes possible to display ananimation without delay.

Further, since the light emitting portion of the light emitting deviceconsumes power, it is preferable to display information so that thelight emitting portion is as small as possible. Therefore, when usingthe light emitting device in the portable information terminal,especially in the display portion where character information is mainlyshown in a portable phone or an audio apparatus, it is preferable todrive so that the character information is formed of a light emittingportion with the non-light emitting portion as a background.

Here, FIG. 15A shows a portable telephone, which contains a main body2601, a sound output portion 2602, a sound input portion 2603, a displayportion 2604, an operation switch 2605 and an antenna 2606. The lightemitting device of this invention can be applied to the display portion2604. Note that, when using the light emitting device to the displayportion 2604, the consumption power of the portable telephone may besuppressed by displaying the character in the light emitting portionwith the background of the non-light emitting portion.

FIG. 15B shows also a portable telephone, but it is a folding twice typedifferent from that of FIG. 15A, and contains a main body 2611, a soundoutput portion 2612, a sound input portion 2613, a display portion (a)2614, a display portion (b) 2615 and an antenna 2616. The operationswitch is not adhered to the portable telephone, but its function isprovided to the portable telephone by displaying a character informationshown in FIGS. 15C, 15D and 15E on either of the display portion (a) or(b). Further, another display portion displays mainly the imageinformation. The light emitting device of this invention can be used asthe display portion (a) 2614 or a display portion (b) 2615.

In the case of the portable telephone shown in FIGS. 15A and 15B, thelight emitting devices used in the display portions are incorporatedwith a sensor by a CMOS circuit (a CMOS sensor), and may be used as anauthentication system terminal for authenticating the user by readingthe fingerprints or the hand of the user. Further, light emission may beperformed by taking into consideration the brightness (illumination) ofoutside and making-information display at a contrast that is alreadyset.

Further, in the case of FIG. 15A, the low power consumption may beattained by decreasing the brightness when using the operating switch2605 and increasing the brightness when the use of the operation switchis finished. Further, the brightness of the display portion 2604 isincreased when a call is received, and low power consumption is attainedby decreasing the brightness during a telephone conversation. Further,when using the telephone continuously, by making it have a function sothat display is turned off by time control unless it is reset, the lowpower consumption is realized. It should be noted that this control maybe operated by hand.

Further, FIG. 15F shows an audio reproduction device, a car mountedaudio in the concrete, which contains a main body 2621, a displayportion 2622, and operation switches 2623 and 2624. The light emittingdevice of this invention can be applied to the display portion 2622.Further, in this embodiment, a car-mounted audio (car audio) is shown,but it may be used in a portable type or domestic type audio (audiocomponent). Note that, when using a light emitting device in the displayportion 2622, by displaying white characters in the light emittingportion with a black background of non-light emitting portion, powerconsumption may be suppressed. It is especially effective for theportable type audio.

In the case of the portable type electronic apparatuses shown in thisembodiment, the sensor portion is provided to perceive the externallight and the function to lower the brightness of the display portion isadded to portable type electronic apparatuses when it is used in thedark area as a method to lower the power consumption.

As in the above, the applicable range of this invention is extremelywide, and may be used for various electrical equipments. Further, theelectrical equipment of this embodiment may use the electronic devicecontaining any of the structures of Embodiments 1 to 5.

By preparing an absorption metal as a film formed on EL elements on theinside of a sealed space, it becomes easier to made the interior of thespace possess an absorption function, and further, an enclosurestructure can be fabricated without the penetration of oxygen andmoisture into the space because the absorption film can be formed insuccession after formation the EL elements with the present invention.

1. A method of manufacturing a light emitting device comprising thesteps of: providing a film formation apparatus; forming a firstelectrode over a substrate in the film formation apparatus; forming anEL layer over the first electrode in the film formation apparatus,wherein the EL layer comprises a hole injecting layer, a holetransporting layer, and a light emitting layer; forming a secondelectrode over the EL layer in the film formation apparatus; forming anabsorption film over the EL layer in the film formation apparatus so asto cover the EL layer; forming a passivation film so as to cover theabsorption film in the film formation apparatus; sealing a region whichis covered with the passivation film by using a sealant and a sealingsubstrate in the film formation apparatus; and covering the sealant andthe sealing substrate with a metallic film under atmospheric pressure,wherein the substrate is prevented from contacting an air outside of thefilm formation apparatus after the formation of the EL layer and untilthe formation of the absorption film is finished, and wherein themetallic film is formed by an evaporation method.
 2. The method ofmanufacturing a light emitting device according to claim 1, wherein theabsorption film is an inorganic hygroscopic film.
 3. The method ofmanufacturing a light emitting device according to claim 2, wherein theinorganic hygroscopic film comprises alkaline-earth metal.
 4. The methodof manufacturing a light emitting device according to claim 2, whereinthe inorganic hygroscopic film has 1 to 3 μm thickness.
 5. The method ofmanufacturing a light emitting device according to claim 1, furthercomprising the step of, forming a barrier film so as to be interposedbetween the second electrode and the absorption film.
 6. The method ofmanufacturing a light emitting device according to claim 5, wherein theprotective electrode is formed from silver.
 7. The method ofmanufacturing a light emitting device according to claim 1, furthercomprising the step of, forming a protective electrode so as to beinterposed between the second electrode and the absorption film.
 8. Themethod of manufacturing a light emitting device according to claim 1,wherein the metallic film is formed under inert condition.
 9. A methodof manufacturing a light emitting device comprising the steps of:forming a first electrode over a substrate; forming an EL layer over thefirst electrode, wherein the EL layer comprises a hole injecting layer,a hole transporting layer, and a light emitting layer; forming a secondelectrode over the EL layer; forming an absorption film over the secondelectrode so as to cover the EL layer; forming a passivation film so asto cover the absorption film; sealing a region which is covered with thepassivation film by using a sealant and a sealing substrate; andcovering the sealant and the sealing substrate with a metallic filmunder atmospheric pressure, wherein layers of the EL layer to theabsorption film are formed in succession, and wherein the metallic filmis formed by an evaporation method.
 10. The method of manufacturing alight emitting device according to claim 9, further comprising the stepof: forming a protective electrode so as to be interposed between thesecond electrode and the absorption film.
 11. The method ofmanufacturing a light emitting device according to claim 10, wherein theprotective electrode is formed from silver.
 12. The method ofmanufacturing a light emitting device according to claim 9, furthercomprising the step of, forming a barrier film so as to be interposedbetween the second electrode and the absorption film.
 13. The method ofmanufacturing a light emitting device according to claim 9, wherein themetallic film is formed under inert condition.